(Invited) All-Solid-State Na- and K-Ion Batteries with Dry Polymer Electrolytes

Abstract

The development of sodium-ion and potassium-ion batteries has gained increasing attention as a sustainable and cost-effective alternative to lithium-ion batteries, due to the abundance of their constituent elements.[1]-[3] All-solid-state batteries offer high safety advantages in high-temperature conditions, as their solid composition reduces the risk of leakage or ignition of the organic electrolyte. As large-scale and stationary batteries for energy storage applications require safety and durability in wide-temperature operations, all-solid-state sodium-ion and potassium-ion batteries can provide a potential solution.This study presents the fabrication of all-solid-state sodium batteries, using dry polymer electrolytes, optimized for stable operation at 60 °C.[4] A composite electrode with uniformly dispersed conductive carbon and binder polymer is essential to achieve a stable charge-discharge reaction in all-solid-state cell, due to the absence of the liquid electrolyte penetrated in the electrode pores. The use of a polymer electrolyte as a binder polymer provides an effective ionic conduction path inside the electrode, which allows stable charge-discharge reaction even at the thick composite electrodes. The fabricated all-solid-state Na // P2-Na2/3[Ni1/3Mn2/3]O2 cell exhibits superior cycle performance at 60 °C, compared to the liquid electrolyte. Furthermore, coating P2-Na2/3[Ni1/3Mn2/3]O2 with Al-oxide enhances the capacity retention of the P2-Na2/3[Ni1/3Mn2/3]O2 // hard carbon full cell, with a mean discharge voltage of 3.11 V and energy density of 148 Wh (kg of active material)−1. To the best of our knowledge, this is the highest value ever reported for full-cell operation of an all-solid-state sodium-ion battery using a dry-polymer electrolyte.The study also reports the fabrication of all-solid-state potassium batteries, where the effects of K metal pretreatment on the K metal/solid polymer electrolyte interface were investigated.[5] The use of K metal chunk, pretreated with the electrolytes containing potassium bis(fluorosulfonyl)amide (KFSA), effectively suppressed polarization and interfacial resistance during continuous K metal stripping-deposition reactions in the cross-linked polymer electrolyte, poly[ethylene oxide-co-2-(2-methoxyethoxy)ethyl glycidyl ether-co-allyl glycidyl ether] (P(EO/MEEGE/AGE)). The addition of 1,3,2-dioxathiolane 2,2-dioxide (DTD) to the pretreatment solution further decreased polarization and interfacial resistance, due to the formation of a stable passivation layer on K metal by FSA− ions and DTD. The efficient operation of the potassium iron hexacyanoferrate positive electrode and graphite negative electrode in P(EO/MEEGE/AGE), with the K metal counter electrode, was achieved by effectively suppressing interfacial resistance through pretreatment. Stable K metal counter electrode for all-solid-state potassium cell was also beneficial to design full cell of all-solid-state potassium-ion cell, enabling us to fabricate the first 3 V-class all-solid-state K-ion battery operated at room temperature.